Round robin: optimize for equal distribution

[TymonSliwinski]

Is your proposal related to a problem?

Optimizing for equal distribution allows for the most even distribution of meetings across hosts. This way no member will be behind in number of meetings.

Describe the solution you'd like

Calendly has their own solution here

[PeerRich]

this is almost done @TymonSliwinski

[emrysal]

This got very complicated very quickly in the old slot logic, but we've rewritten that from scratch - a new version of this pr will go in in 3.2